Speed control device

ABSTRACT

In a speed control system, there are provided a speed observer compensator ( 10 ) for inputting a difference between a speed V M  of a mechanical system ( 5 ) and an estimated value V MO  of a speed of the mechanical system ( 5 ) which is obtained by a speed observer ( 6 ) and outputting a speed difference V M −V MO  based on the input, and a mechanical system model ( 8 ) for inputting a sum of an output of the speed observer compensator ( 10 ) and an output T ro  of a PI controller ( 2 ), and the speed observer ( 6 ) is constituted in such a manner that the signal V MO  produced after a passage of an output of the mechanical system model ( 8 ) through a filter delay element model ( 11 ) and a dead time delay element model ( 12 ) is equal to the speed V M  of the mechanical system ( 5 ), and the output of the mechanical system model ( 8 ) is set to be a speed feedback signal V f  of the speed control system. Consequently, it is possible to provide a speed control device capable of removing the high frequency component of the speed feedback signal, compensating for the phase delay of the delay element so as not to generate an oscillation having a high frequency, and causing the speed of the mechanical system to follow a target speed with high precision.

TECHNICAL FIELD

The present invention relates to a speed control device capable ofconstituting a speed observer including the delay element of a controlsystem and setting the estimated value of a non-delayed speed of thespeed observer to be a speed feedback signal, thereby removing the highfrequency component of the speed feedback signal and increasing theresponse performance of the control system by one stage.

BACKGROUND ART

In general, a speed control system in which a filter delay element or adead time delay element is present in a controller or a control objectis shown in FIG. 3. FIG. 3 is a block diagram showing a general speedcontrol system.

In FIG. 3, 1 denotes a subtractor, 2 denotes a PI controller, 3 denotesa filter delay element, 4 denotes a dead time delay element, 5 denotes amechanical system including a motor, V_(r) denotes a target speed, V_(f)denotes a speed feedback signal, and V_(M) denotes a speed.

In a general speed control device, both a speed signal obtained from aspeed sensor (not shown) and a speed signal obtained by differentiatinga position signal of a position sensor (not shown) have high frequencyripple components. Also in the control system shown in FIG. 3,therefore, the speed feedback signal V_(f) has the high frequency ripplecomponent, and furthermore, the phase of the filter delay element 3 orthe dead time delay element 4 is delayed. For this reason, there is aproblem in that the gain of the PI controller 2 is not increased and asufficient response characteristic cannot be obtained. In order toimprove such a problem of controllability, the following conventionalart has been proposed.

FIG. 4 is a block diagram showing a control system according to a firstconventional art. The same components in the first conventional art asthose in FIG. 3 have the same reference numerals and description will beomitted, and only different components will be described. In FIG. 4, 7denotes an adder, 8 denotes a model of a mechanical system including amotor, 9 denotes a subtractor, 10 denotes a speed observer compensator,and 14 denotes a speed observer. As shown in FIG. 4, an observer of themechanical system is constituted and a speed estimated value of thesmooth observer is set to be a speed feedback signal V_(f).Consequently, a torque waveform is not disturbed so that the gain of thePI controller 2 can be increased (for example, JP-A-11-136983).

Moreover, FIG. 5 is a block diagram showing a control system accordingto a second conventional art. Components in the second conventional artare different from those in FIG. 3 in that a phase leading compensator13 is added in series to a control system. In the phase leadingcompensator 13, if T_(a) and T_(b) are properly set to be T_(a)>T_(b),the phase of the phase leading compensator 13 is led. Consequently, thegain of the PI controller 2 can be increased, and furthermore, a controlperformance can be enhanced.

In the first conventional art, however, the high frequency component ofthe speed feedback signal V_(f) is removed and a problem of the phasedelay of a control loop is not solved at all. For this reason, there isa problem in that the gain of the PI controller 2 cannot be increasedsufficiently.

In the second conventional art, moreover, a gain in the high frequencyarea of the phase leading compensator 13 is increased. Consequently,there is a problem in that an oscillation having a high frequency is aptto be caused.

In order to solve the problems, it is an object of the invention toprovide a speed control device capable of removing the high frequencycomponent of a speed feedback signal, compensating for the phase delayof a delay element so as not to generate an oscillation having a highfrequency, and causing the speed of a mechanical system to follow atarget speed with high precision.

DISCLOSURE OF THE INVENTION

In order to solve the problems, the invention provides a speed controldevice to be a speed control system in which a filter delay element (3)or a dead time delay element (4) is present in a controller or a controlobject and a PI control is carried out to follow a speed command to be atarget speed V_(r), comprising a speed observer compensator (10) forinputting a difference between a speed V_(M) of a mechanical system (5)and an estimated value V_(MO) of a speed of the mechanical system (5)which is obtained by a speed observer (6) and outputting a speeddifference V_(M)−V_(MO) based on the input, and a mechanical systemmodel (8) for inputting a sum of an output of the speed observercompensator (10) and an output T_(ro) of a PI controller (2), whereinthe speed observer (6) is constituted in such a manner that the signalV_(MO) produced after a passage of an output of the mechanical systemmodel (8) through a filter delay element model (11) and a dead timedelay element model (12) is equal to the speed V_(M) of the mechanicalsystem (5), and the output of the mechanical system model (8) is set tobe a speed feedback signal V_(f) of the speed control system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the principle of the structure ofa control system according to an embodiment of the invention.

FIG. 2 is an equivalent block diagram in FIG. 1.

FIG. 3 is a block diagram showing an ordinary feedback control system.

FIG. 4 is a block diagram showing a control system according to a firstconventional art.

FIG. 5 is a block diagram showing a control system according to a secondconventional art.

BEST MODE OF CARRYING OUT THE INVENTION

An embodiment of the invention will be described with reference to thedrawings.

FIG. 1 is a block diagram showing the principle of the structure of acontrol system according to the embodiment of the invention. The samecomponents of the invention as those of the conventional art have thesame reference numerals and description will be omitted, and onlydifferent components will be described.

In FIG. 1, 11 denotes a filter delay element model, 12 denotes a deadtime delay element model, and 6 denotes a speed observer.

The invention is different from the conventional art as follows.

More specifically, in a speed control system in which a filter delayelement 3 or a dead time delay element 4 is present in a controller or acontrol object and a PI control is carried out to follow a speed commandto be a target speed V_(r), comprising a speed observer compensator 10for inputting a difference between a speed V_(M) of a mechanical system5 and an estimated value V_(MO) of a speed of the mechanical system 5which is obtained by a speed observer 6 and outputting a speeddifference V_(M)−V_(MO) based on the input, and a mechanical systemmodel 8 for inputting a sum of an output of the speed observercompensator 10 and an output T_(ro) of a PI controller 2, the speedobserver 6 is constituted in such a manner that the signal V_(MO)produced after a passage of an output of the mechanical system model 8through a filter delay element model 11 and a dead time delay elementmodel 12 is equal to the speed V_(M)of the mechanical system 5, and theoutput of the mechanical system model 8 is set to be a speed feedbacksignal V_(f) of the speed control system.

Next, an operation will be described.

In FIG. 1, the output T_(ro) of the PI controller 2 and the output ofthe speed observer compensator 10 are added and input to the mechanicalsystem model 8 (including a motor). The output of the mechanical systemmodel 8 (including the motor) is set to be the speed feedback signalV_(f) of the control system, and a signal obtained by subtracting thespeed feedback signal V_(f) from the target speed V_(r) is input to thePI controller 2 and the output T_(ro) of the PI controller 2 is input tothe mechanical system (including the motor) through the filter delayelement 3 and the dead time delay element 4 to control the mechanicalsystem (including the motor), while the same output is input to asubtractor 9 through the filter delay element model 11 and the dead timedelay element model 12 and is then subtracted from the speed V_(M) ofthe mechanical system (including the motor), and a signal thus obtainedis input to the speed observer compensator 10.

Referring to FIG. 1, in an open loop, a transfer function from theoutput T_(ro) of the PI controller 2 to the speed feedback signal V_(f)is expressed in the following Equation (1).

$\begin{matrix}{\frac{V_{f}(s)}{T_{r\; 0}(s)} = \frac{1}{{Js} + D}} & {{Eq}.\mspace{14mu}(1)}\end{matrix}$

If the closed loop of the speed observer is stable, therefore, thecontrol system in FIG. 1 can be rewritten equivalently as shown in FIG.2. FIG. 2 is an equivalent block diagram in FIG. 1. Referring to FIG. 2,the stability of a feedback control system is the same as that of asystem having no delay. Even if the gain of the PI controller isincreased greatly, the control system can be prevented from beingunstable. Moreover, a transfer function from the target speed V_(r) tothe speed V_(M) of the mechanical system is expressed in the followingEquation (2).

$\begin{matrix}{\frac{V_{M}(s)}{V_{r}(s)} = {{\frac{{K_{p}s} + K_{i}}{{Js}^{2} + {( {D + K_{p}} )s} + K_{i}} \cdot \frac{1}{1 + {T_{f}s}}}{\mathbb{e}}^{{- T_{d}}s}}} & {{Eq}.\mspace{14mu}(2)}\end{matrix}$

Thus, it is possible to cause the speed V_(M) of the mechanical systemto follow the target speed V_(r) with high precision by increasing gainsK_(p) and K_(i) of the PI controller 2. Moreover, the loop of the speedobserver has a delay element and an input/output characteristic is notrelated to a compensator C_(o) (s) of the speed observer based on theEquation (2). Therefore, the gain of the compensator C_(o) (s) of thespeed observer may be set to be small. Accordingly, a stable speedobserver can be constituted easily.

Therefore, the invention provides the speed control system in which thefilter delay element 3 or the dead time delay element 4 is present in acontroller or a control object and a PI control is carried out to followa speed command to be the target speed V_(r), comprising the speedobserver compensator 10 for inputting a difference between the speedV_(M) of the mechanical system 5 and the estimated value V_(MO) of aspeed of the mechanical system 5 which is obtained by the speed observer6 and outputting the speed difference V_(M)−V_(MO) based on the input,and the mechanical system model 8 for inputting a sum of an output ofthe speed observer compensator 10 and the output T_(ro) of the PIcontroller 2, wherein the speed observer 6 is constituted in such amanner that the signal V_(MO) produced after a passage of an output ofthe mechanical system model 8 through the filter delay element model 11and the dead time delay element model 12 is equal to the speed V_(M) ofthe mechanical system 5, and the output of the mechanical system model 8is set to be the speed feedback signal V_(f) of the speed controlsystem. Therefore, the speed observer including the delay element of thecontrol system is constituted and the estimated value of a non-delayedspeed of the speed observer is set to be the speed feedback signal.Consequently, the high frequency component of the speed feedback signalcan be removed.

Moreover, the control system is divided into a feedback control sectionand a speed observer section. Consequently, the stability of thefeedback loop is the same as that of a system having no delay so thatthe gain of the PI controller can be increased greatly. Thus, theresponse performance of the control system can be enhanced by one stage.

Although the loop of the speed observer has the delay element,furthermore, the compensator of the speed observer does not influencethe input/output characteristic. Therefore, the gain of the compensatorof the observer may be set to be small. Consequently, the stableobserver can be constituted easily. More specifically, the highfrequency component of the speed feedback signal is removed and thephase delay of the delay element is compensated so as not to cause anoscillation having a high frequency. Therefore, the gain of the PIcontroller can be increased and the speed of the mechanical system canbe caused to follow the target speed with high precision.

INDUSTRIAL APPLICABILITY

As described above, the speed control device according to the inventionis useful to be utilized for a speed control device of an electric motorin which a filter delay element or a dead time delay element is presentin a controller or a control object.

1. A speed control device comprising: a speed control system including afilter delay element or a dead time delay element in a controller or acontrol object, the speed control system operable to carry out a PIcontrol to follow a speed command to be a target speed V_(r); a speedobserver generating a speed difference V_(M)−V_(MO) which is adifference between a speed V_(M) of a mechanical system and an estimatedvalue V_(MO) of a speed of the mechanical system; a speed observercompensator receiving the speed difference, a mechanical system modelreceiving sum of an output of the speed observer compensator and anoutput T_(ro) of a PI controller; wherein the speed observer isconstituted in such a manner that the signal V_(MO) produced after apassage of an output of the mechanical system model though a filterdelay element model and a dead time delay element model is equal to thespeed V_(M) of the mechanical system, and wherein an output of themechanical system model is provided as a speed feedback signal V_(f) ofthe speed control system.